The paper describes high output induction motors driving large
applications of heavy starting conditions. Heavy start is characterised
by long accelerating time and occures in drives of hudge inertia torque,
esspecially when performed at full load. The reliable operation of the
motors depends on proper design and quality of rotor's cage. The aspects
of thermal behaviour and electrodynamic forces have to be considered
during the design of the motor for hard working conditions. In the paper
the rotor with idle bars is investigated.